Word order makes no difference. Pluperfects (even periphrastic ones)
indicate action that precede the action described by the main verb. The
Verb-Subject word order (the hOSOI HSAN TETAGMENOI clause serves as the
grammatical subject of the verb EPISTEUSAN) is well within norms of Biblical
Greek cf Moulton III 344ff.

First the assignment, then the believing. Passive no doubt out of respect
to the Divine doer of the action of assigning.